Terrestrial ecosystems serve as significant sources and sinks for various gases, such as carbon dioxide (CO2). In natural forest ecosystems, CO2 is generally absorbed through the forest canopy as photosynthesis occurs and emitted back into the atmosphere through the respiration of living organisms, with as much as 50% or more being emitted by decay bacteria and fungi as they decompose tissues in the forest soil. Tree roots, living woody tissue as well as night-time respiration of foliage also contribute to the efflux of CO2 from forest systems. As the forest matures and its canopy grows, the level of carbon influx may exceed the level of carbon efflux. Forests typically move from being sources of atmospheric carbon after a disturbance that removes the canopy, i.e. forest operations or fire, to a sink of carbon at some later stage of maturity. We are now in an age where carbon pool management is being politicized and legislated while the role soil respiration (combination of respiration of soil microbes and living roots) plays in carbon budgets continues to be refined. This is of particular interest in both agricultural systems and managed forest ecosystems, where management/cultural decisions may have a substantial impact on the net carbon balance. Cultural practices, site preparation, nutritional amendments and genetic improvement all have the potential to influence net ecosystem productivity and affect carbon sequestration.
The measurement of soil, woody debris, root and stem respiration is essential to understanding the loss of carbon in the ecosystem. Early sampling techniques measured carbon loss using closed, static chambers placed on the soil surface and the rate of CO2 accumulation was assessed by measuring the amount of CO2 captured in an alkali trap (KOH, NaOH, or Soda Lime) over a fixed period of time. Other alternative static methods require the periodic drawing of samples from the soil so as to measure its carbon concentration with gas chromatography and compute its carbon flux rate over the collection period.
These static methods, however, suffer from several drawbacks. For instance, they are exceptionally burdensome to technicians taking diurnal carbon efflux measures, who are required to manually perform each measurement individually, in single chambers. Additionally, the accumulation of high concentrations of CO2 in the collection chambers results in a greater storage of CO2 in the soil, which changes the soil""s CO2 diffusion paths, and results in a reduction in the soil""s respiration rate over time. These limitations hinder the studying of CO2 efflux changes in dynamic terrestrial ecosystems.
What is therefore needed is a better system which provides for the accurate, continuous measurement of soil and woody tissue respiration rates as they fluctuate diurnally and seasonally.
In accordance with a first aspect of the invention, an apparatus for measuring the efflux of gas from a substrate includes an inspection system having at least one air pump and a data analysis system. At least one measuring chamber has a substrate disposed therein that produces a quantity or a gas. A conduit system is attached to the measuring chamber at one end and to the inspection system at a second end. The at least one air pump supplies reference air having a known quantity of the gas to the at least one chamber via the conduit system so as to mix the reference air with the gas to produce a mixed air. The mixed air is then sent to the inspection system via the conduit system, and the data analysis system is able to measure the unknown quantity of gas.
These as well as other features and characteristics of the present invention will be apparent from the description which follows. In the detailed description below, preferred embodiments of the invention will be described with reference to the accompanying drawings. These embodiments do not represent the full scope of the invention. Rather the invention may be employed in other embodiments. Reference should therefore be made to the claims herein for interpreting the breadth of the invention.